* Declare vtb_buffer as a pointer to uint16_t and get rid of

* Declare vtb_buffer as a pointer to uint16_t and get rid of
  sc_vtb_pointer() and some casts.

* Use the standard uint16_t type instead of u_int16_t.

* Use M_ZERO instead of explicitly bzero()ing.

* Don't set VTB_VALID if malloc() failed.

In discussion with: joerg